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142                            STRUCTURE   OF   KOALA                           CHAP.
species of the genus, which extend through pretty well the
entire Australian region. The term " flying " as applied to these
and the other " flying " genera is of course an exaggeration. The
animals cannot fly upwards; they can only descend in a skim-
ming fashion, the folds of skin breaking their fall. -P. breviceps is
perhaps the best - known species. The body is 8, the tail 9
inches long.
PetauToides seems to be chiefly distinguished from Petaurus
by the fact that, as in its ally Dactylopsila, the tail is partly
naked terminally. In Petaurus and Gymnobelideus the tail is
bushy to the very end, including its extreme tip below.
A third genus of Flying Phalangers is the minute Acrobates,
which has a distichous tail like that of Distaecliwrus. It is not
more than 6 inches in length including the tail. As to these
Flying Phalangers it is exceedingly instructive to observe that
the same method of " flight" has been apparently evolved three
times; for the three genera are each of them specially related
to a separate type of non-flying Phalanger. The same observa-
tion can be made about the Flying Squirrels, Anomalurus and
Sciuropter^. The dental formula is 11- C -J- Pm -§- M -§-. The
ears are thinly clad with hair. There are four teats.
Sub-Fam. 2. Piiaseolarctinae,—The Koala, or Native Bear,
Phascolarctos cinereus, is the only representative of its sub-family.
It is, like the Wombat, aberrant in the lack of an obvious tail.
The absence of this appendage is curious in an arboreal creature
whose near allies have a long and prehensile one. The structure
of the Koala was investigated by the late Mr. "W. A. Forbes.1
There are some unexpected points of likeness to the "Wombat:
thus they agree in the absence of the tail, in the structure of the
stomach, and in the great subdivision of the lobes of the liver.
The brain, however, is smooth, and the caecum is exceedingly large
and complicated in structure., that of the Wombat being short.
That both animals have cheek-pouches is perhaps due to similar
habits of temporarily storing masses of food. This animal has
only eleven pairs of ribs. The tail has only seven or eight verte-
bra, and these have no chevron-bones.                           >
A peculiarity of the skull is seen in the great size of the
alisphenoid bulla, which is comparable in size and appearance with,
that of the Pig, As in the Kangaroos, the atlas is incomplete below.
* **On. some Points in the Anatomy of the Koala," JProc. Zool. Soc. I8S1. r>. lfto